Multiblade fan

ABSTRACT

To provide a multiblade fan that enables an improvement in noise characteristics or blowing performance. The multiblade fan includes a scroll type casing that has a bell-mouthed inlet and an impeller housed in the casing. The impeller includes a plurality of blades and a rotation axis m oriented toward the inlet of the casing. The blades are annularly arranged. In the multiblade fan, a center axis of the inlet and the rotation axis of the impeller are arranged at a tilt angle to each other and in any one of an intersecting positional relationship and a skew-lines positional relationship so that a space between the inlet and the impeller increases from the rotation axis of the impeller toward an outlet of the casing.

TECHNICAL FIELD

The present invention relates to a multiblade fan, and moreparticularly, to a multiblade fan capable of improving noisecharacteristics or blowing performance.

BACKGROUND ART

A typical multiblade fan includes a scroll type casing having abell-mouthed inlet and an impeller housed in the casing. The impeller isa multiblade impeller (sirocco fan) that includes a plurality ofannularly arranged blades and that is housed in the casing with arotation axis of the impeller oriented toward the inlet of the casing.

In a structure where a center axis of the inlet and the rotation axis ofthe impeller are coaxially arranged, an inertial force is exerted on airflown into the impeller through the inlet. Hence, airflow inside theimpeller is likely to be deflected toward a main plate (a plate thatsupports blades). Then, the velocity distribution (velocity distributionof air blowing out of the spaces between the blades) of the air passingthrough between the blades (space between the blades) becomes nonuniformin the axial direction of the impeller. Because this causes the velocityof flow to be likely to fluctuate, pressure differential of air or alevel of air turbulence increases, which can result in louder noise ordegradation in blowing performance.

When the multiblade fan is constructed in this manner, air is incidenton a blade at an acute (sharp) incident angle when the air flows intothe impeller to pass through between the blades. Because this causes theimpeller to function insufficiently, it is possible that the multibladefan provides its blowing performance insufficiently.

In view of the above circumstances, conventional multiblade fans haveadopted a configuration in which an inlet is deformed depending on aninflow velocity of air (see Patent Document 1), a configuration in whichend portions of blades are tapered (see Patent Document 2), and thelike. In the multiblade fans having these configurations, an airflowrate near the end portions of the blades is increased, making velocitydistribution of air inside an impeller uniform. This improvesperformance of the blowers.

Another conventional multiblade fan has adopted a configuration ofcausing a space between an impeller and a bell-mouthed inlet to vary ina rotation direction (see Patent Document 3). This configuration makesvelocity distribution of air inside the impeller uniform, therebyimproving performance of the blower. However, these configurations aredisadvantageous in that because the shape of a casing is complicated orit is difficult to release the casing from a die, cost of productionincreases.

The multiblade fan uses a scroll type casing that is expanded by apredetermined degree to recover a static pressure. Accordingly, when aposition where air is sucked is changed, velocity of airflow inside theimpeller is changed, thereby changing the deflection of the airflow thatis deflected toward the main plate. Hence, changing the shape of theblades of the impeller is disadvantageous in being insufficientlyeffective. This is because the changing the shape of the blades iseffective for a target airflow; however, there are produced losses inair flows other than the target airflow. It is also necessary todetermine the shape of the blades while taking its influences over anall-around rotation of the impeller into consideration.

PRIOR ART DOCUMENT Patent Document

-   Patent document 1: Japanese Patent Application Laid-open No.    2000-179496-   Patent document 2: Japanese Patent Application Laid-open No.    2006-200525-   Patent document 3: Japanese Patent Application Laid-open No.    1995-228128

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

It is an object of the present invention to provide a multiblade fancapable of improving noise characteristics or blowing performance.

Means for Solving Problem

To achieve the object, a multiblade fan according to the presentinvention includes a scroll type casing that includes a bell-mouthedinlet and an impeller that includes a plurality of annularly arrangedblades and a rotation axis oriented toward the inlet and that is housedin the casing. A center axis of the inlet and the rotation axis of theimpeller are arranged to make a tilt angle and in either one of amutually intersecting positional relationship and a mutually skewedpositional relationship, so that a space between the inlet and theimpeller is increased from the rotation axis of the impeller toward anoutlet of the casing.

Effect of the Invention

In a multiblade fan according to an aspect of the present invention, aspace between an inlet and an impeller increases from a rotation axis ofthe impeller toward an outlet of a casing. This configuration permitsair that has flown into the impeller through the inlet to flow in agentle curve inside the impeller to pass through between blades. Thiscauses velocity distribution (deflection of airflow) of intake airinside the impeller and an incident angle of the intake air on a bladeto relatively change, thereby making the velocity distribution of airhaving passed through between the blades uniform in the axial directionof the rotation axis of the impeller. Hence, the noise characteristicsand the blowing performance are advantageously improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional plan view depicting a multibladefan according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view taken along line A-A of themultiblade fan depicted in FIG. 1.

FIG. 3 is a schematic explanatory diagram illustrating how themultiblade fan depicted in FIG. 1 works.

FIG. 4 is a schematic explanatory diagram illustrating how themultiblade fan depicted in FIG. 1 works.

FIG. 5 is a graph illustrating noise characteristics for differentspaces between an inlet and an impeller.

FIG. 6 is a graph illustrating results of performance tests ofmultiblade fans.

FIG. 7 is a graph illustrating results of performance tests ofmultiblade fans.

FIG. 8 is a schematic explanatory diagram of the configuration of themultiblade fan depicted in FIG. 1.

FIG. 9 is a schematic explanatory diagram of a modification of themultiblade fan depicted in FIG. 1.

FIG. 10 is a schematic explanatory diagram of another modification ofthe multiblade fan depicted in FIG. 1.

FIG. 11 is a schematic configuration diagram of a conventionalmultiblade fan.

FIG. 12 is a schematic explanatory diagram illustrating how themultiblade fan depicted in FIG. 11 works.

BEST MODES FOR CARRYING OUT THE INVENTION

Exemplary embodiments of the present invention are described in detailbelow with reference to the accompanying drawings. The present inventionis not limited to the exemplary embodiments. Elements of the embodimentsinclude all equivalents that do not depart from the spirit and scope ofthe invention in its broadest form. The plurality of modifications ofthe embodiments mentioned below can be arbitrarily combined within therange that will occur to those skilled in the art.

[Multiblade Fan]

A multiblade fan 1 is a blower that includes a multibladed wheel(sirocco fan). The multiblade fan 1 is applied to, for example, an airconditioning system, a duct fan, and a ventilating fan. The multibladefan 1 can be of a single inlet type or a double inlet type. In thepresent embodiment, the multiblade fan 1 of a single inlet type will bedescribed as an example.

The multiblade fan 1 includes a casing 2, an impeller 3, and a drivemotor 4 (see FIG. 1 and FIG. 2).

The casing 2 is, for example, a scroll type casing. The casing 2includes a main body 21, an inlet 22, and an outlet 23. The main body 21assumes a scroll-like shape in plan view. The inlet 22 is a bell-mouthedinlet defined in a side surface (axially upper surface of thescroll-like shape) of the main body 21, at a center of the scroll-likeshape. The outlet 23 is defined in a circumferential surface (coiledsurface of the scroll-like shape) of the main body 21. The casing 2 ismade of, for example, resin and formed by die molding.

The impeller 3 is a multibladed wheel (sirocco fan) that includes aplurality of blades 31 that are annularly arranged. The impeller 3includes a rotary shaft m that is oriented toward the inlet 22 of thecasing 2 and a circumferential surface that is oriented along thecircumference of the casing 2. For example, in the present embodiment,the impeller 3 is constructed by annularly arranging the blades 31 alongthe rim of a substantially disc-shaped main plate 32 at predeterminedintervals and fixing the blades 31 to the main plate 32. In this manner,a bladed wheel made of the blades 31 is formed on the main plate 32. Anannular member 33 serving as reinforcement is fit in end portions (endportions on the side opposite from the main plate 32) of the blades 31.The impeller 3 is housed in the casing 2 with the end portions of theblades 31 oriented toward the inlet 22 and with a circumferentialsurface of the bladed wheel oriented along the circumference of thecasing 2.

The drive motor 4 is a motor that drives the impeller 3 to rotate. Thedrive motor 4 is inserted into the casing 2 through the bottom surfaceof the casing 2 to be coupled to the main plate 32 of the impeller 3.On/off control of the drive motor 4 is performed by using, for example,an external switch.

When the drive motor 4 is driven to rotate the impeller 3, air is suckedinto the main body 21 through the inlet 22 of the casing 2. The airpasses through the multiblade fan 1 such that air pressure is increasedby the impeller 3 and then recovered to a static pressure through thescroll-like shape of the casing 2, and then the air is blown out to theoutside through the outlet 23 of the casing 2. Air is blown by themultiblade fan 1 in this manner.

[Positional Relationship Between Inlet and Impeller]

Generally, (1) in a configuration where a center axis l of an inlet anda rotation axis m of an impeller are coaxially arranged, an inertialforce is exerted on air that have flown into the impeller through theinlet (see FIG. 11). This makes airflow inside the impeller to bedeflected toward a main plate. When the airflow is deflected in thismanner, velocity distribution (velocity distribution of air blowing outof spaces between the blades) of air that passes through between blades(the spaces between blades) of the impeller becomes nonuniform in theaxial direction of the impeller. Because this makes the airflow velocityto be likely to fluctuate, pressure differential of air or a level ofair turbulence increases, which can result in louder noise, blowingperformance degradation, or the like. This configuration also causes (2)air to be incident on a blade at an acute (sharp) incident angle δ whenthe air flows into the impeller to pass through between blades (see FIG.12). Because this causes the impeller to function insufficiently, it ispossible that the multiblade fan fails to provide its blowingperformance sufficiently.

To this end, in the multiblade fan 1, the center axis l of the inlet 22of the casing 2 and the rotation axis m of the impeller 3 are arrangedin (a) an intersecting positional relationship where they intersect witheach other at a tilt angle φ or in (b) a skew-lines positionalrelationship where they are skewed relative to each other (see FIG. 2).In other words, the positional relationship between the inlet 22 and theimpeller 3 are set such that the center axis l of the inlet 22 and therotation axis m of the impeller 3 are not coaxial with each other (noton a single axis). Meanwhile, the center axis l of the inlet 22 is acenter axis of the bell-mouthed inlet of the inlet 22.

A space L between the inlet 22 and the blades 31 of the impeller 3increases toward the outlet 23 of the casing 2 due to the positionalrelationship between the inlet 22 and the impeller 3 (see FIG. 1 andFIG. 2). For example, in the present embodiment, the space L between anopening surface of the inlet 22 and an end (an end of one of the blades31 near the inlet 22) of the one of the blades 31 of the impeller 3increases from the rotation axis m of the impeller 3 toward the outlet23 of the casing 2. The space L can be arbitrarily set according tospecifications for the multiblade fan 1 or the like.

When the multiblade fan 1 is configured in this manner, because thespace L between the inlet 22 and the impeller 3 increases from therotation axis m of the impeller 3 toward the outlet 23 of the casing 2,air that has flown into the impeller 3 through the inlet 22 is allowedto flow in a gentle curve inside the impeller 3 (see FIG. 3). When airflows in this manner, an airflow rate around the blades 31 near theinlet 22 increases. Accordingly, velocity distribution of air thatpasses through between the blades 31, 31 is more uniform in the axialdirection of the impeller 3 as compared with that of the configurationin which airflow is deflected toward the main plate (see FIG. 11). Thisresults in an improvement in noise characteristics and blowingperformance.

This configuration also causes air to flow into the blades 31 at a lessacute incident angle δ inside the impeller 3 (see FIG. 4). Accordingly,the velocity distribution of air that passes through between the blades31, 31 is more uniform as compared with that of the configuration inwhich air flows into the blades at the acute (sharp) angle δ (see FIG.12). Hence, the impeller 3 can provide its function sufficiently,thereby improving blowing performance of the multiblade fan 1.

In the casing 2 that has the scroll-like shape, an opening area of anair passage in the main body 21 is maximized near the outlet 23 (seeFIG. 1). This causes air near the outlet 23 to flow at a relatively highairflow rate, thereby increasing an airflow rate of air that passesthrough between the blades 31 of the impeller 3, which increases themagnitude of the inertia force. As a result, the velocity distributionof the air that passes through between the blades 31, 31 is furtherdeflected toward the main plate. Hence, by increasing the space Lbetween the inlet 22 and the impeller 3 at this position toward theoutlet 23 (see FIG. 2), the velocity distribution of intake air insidethe impeller 3 and the incident angle δ on one of the blades 31 arechanged by a large extent. This makes the velocity distribution, whichcan otherwise be largely deflected toward the main plate, of the airpassing through between the blades 31, 31 effectively uniform.Accordingly, noise characteristics are efficiently improved.

Meanwhile, it is preferable to set the position where the space Lbetween the inlet 22 and the impeller 3 is maximized as required basedon the scroll-like shape of the casing 2 or the like. For example, anarc angle θ [°]that indicates a rotation angle of the impeller 3 aboutthe rotation axis m of the impeller 3 relative to a reference direction,which is parallel to the axial direction of the outlet 23 of the casing2 in plan view of the impeller 3, can be defined (see FIG. 1). The arcangle θ can be set so that favorable noise characteristics are obtainedwith the configuration depicted in FIG. 2 (the configuration in whichthe center axis l of the inlet 22 of the casing 2 and the rotation axism of the impeller 3 are arranged at the tilt angle φ to each other andin any one of the intersecting positional relationship and theskew-lines positional relationship).

FIG. 5 depicts a relationship between the arc angle θ and the noisecharacteristics. In the drawing, the noise characteristics are given asa difference in noise level relative to a reference noise level (0[dB]), which is a noise level of the conventional example. Meanwhile,the conventional example has the configuration in which the center axisl of the inlet and the rotation axis m of the impeller are coaxiallyarranged (φ=0) (see FIG. 11). As depicted in the drawing, the noisecharacteristics are improved most where θ=270 [°], in which θ is the arcangle. This position corresponds to the position near the outlet 23 ofthe casing 2. Accordingly, it is revealed that by setting the space Lbetween the inlet 22 and the impeller 3 to be maximized near the outlet23 of the casing 2, the noise characteristics of the multiblade fan 1are efficiently improved.

[Performance Test]

FIG. 6 and FIG. 7 are graphs illustrating results of performance testsof the multiblade fans. Performance tests for (1) blowing performance(performance measured by static pressure) and (2) noise characteristicshave been performed on the present embodiment.

The multiblade fan of the conventional example subjected to theperformance tests has the configuration in which the center axis l ofthe inlet and the rotation axis m of the impeller are coaxially arranged(φ=0) (see FIG. 11). The multiblade fan 1 of the present embodiment hasthe configuration in which the center axis l of the inlet 22 of thecasing 2 and the rotation axis m of the impeller 3 are arranged at thetilt angle φ to each other and in any one the intersecting positionalrelationship and the skew-lines positional relationship as well as inwhich the space L between the inlet 22 and the impeller 3 is maximizednear the outlet 23 of the casing 2 (θ=270 [°]) (see FIG. 1 and FIG. 2).

As illustrated in the results of the tests, the multiblade fan 1 of thepresent embodiment is improved in blowing performance and noisecharacteristics as compared with the multiblade fan of the conventionalexample. For example, the multiblade fan 1 of the present embodiment isincreased in static pressure by approximately 10 [Pa] and decreased innoise level by approximately 1 [dB] under the same airflow rate.

[Effect]

As described above, this multiblade fan 1 is constructed such that (1)the space L between the inlet 22 and the impeller 3 increases from therotation axis m of the impeller 3 toward the outlet 23 of the casing 2(see FIG. 1 and FIG. 2). This configuration permits air that has flowninto the impeller 3 through the inlet 22 to flow in a gentle curveinside the impeller 3 to pass through between the blades 31, 31 (seeFIG. 3). When air flows in this manner, the velocity distribution(deflection of airflow) of intake air inside the impeller 3 and theincident angle δ of the intake air on one of the blades 31 arerelatively changed, thereby making the velocity distribution of airhaving passed through between the blades 31, 31 uniform in the axialdirection of the rotation axis of the impeller 3. This advantageouslyimproves the noise characteristics and the blowing performance of themultiblade fan 1.

Particularly near the outlet 23, because an airflow rate of air thatpasses through between the blades 31, 31 of the impeller 3 increases,the magnitude of the inertia force increases, which causes the velocitydistribution of the air that passes through between the blades 31, 31 tobe more deflected toward the main plate. Accordingly, by setting thespace L between the inlet 22 and the impeller 3 at this position large,the velocity distribution of intake air inside the impeller 3 and theincident angle δ of the intake air on the one of the blades 31 arechanged by a large extent. As a result, the velocity distribution, whichcan otherwise be largely deflected toward the main plate, of the airpassing through between the blades 31, 31 is effectively made uniform.This advantageously improves the noise characteristic effectively.

The space L between the inlet 22 and the impeller 3 is adjusted because(2) the center axis l of the inlet 22 and the rotation axis m of theimpeller 3 are arranged at the tilt angle φ to each other and in any oneof the intersecting positional relationship and the skew-linespositional relationship. Put another way, the space L is adjusted byadjusting the positional relationship between the center axis l of theinlet 22 and the rotation axis m of the impeller 3. This space L causesthe velocity distribution of intake air inside the impeller 3 and theincident angle δ on one of the blades 31 to be relatively changed,making the velocity distribution of air passing through between theblades 31, 31 uniform. Hence, there is obtained an advantage that thevelocity distribution of air passing through between the blades 31, 31can be made more uniform with a simple configuration as compared withthat of a configuration in which dimensions and/or shapes of theimpeller and the bell-mouthed inlet are complicatedly changed.

[Modifications]

The multiblade fan 1 can employ any one of the following configurations(see FIG. 8 to FIG. 10) to adjust the positional relationship betweenthe center axis l of the inlet 22 and the rotation axis m of theimpeller 3 (they are arranged at the tilt angle φ to each other and inany one of the intersecting positional relationship and the positionalrelationship).

FIG. 8 depicts a configuration in which both the center axis l of theinlet 22 and the rotation axis m of the impeller 3 are tilted relativeto the main body 21, thereby adjusting the positional relationship (tiltangle φ) between the center axis l of the inlet 22 and the rotation axism of the impeller 3. This configuration is advantageous in that the tiltangle φ can be attained more easily in terms of design as compared witha configuration in which only any one of the center axis l of the inlet22 and the rotation axis m of the impeller 3 are tilted relative to themain body 21.

For example, in the present embodiment, a mating portion of an outerperiphery of the bell-mouthed inlet of the inlet 22 and a wall surfaceof the main body 21 includes a stepped portion so that the bell-mouthedinlet of the inlet 22 is tilted relative to the wall surface of the mainbody 21 (see FIG. 2). The drive motor 4 is attached to the main body 21such that the rotation axis of the drive motor 4 is tilted relative tothe wall surface of the main body 21. The impeller 3 is attached to thedrive motor 4. Hence, both the center axis l of the inlet 22 and therotation axis m of the impeller 3 are tilted relative to the main body21.

However, the configuration is not limited thereto. Alternatively, thepositional relationship between the center axis l of the inlet 22 andthe rotation axis m of the impeller 3 can be adjusted by arranging onlyany one of the center axis l of the inlet 22 and the rotation axis m ofthe impeller 3 to be tilted relative to the main body 21 (see FIG. 9 andFIG. 10).

For example, FIG. 9 depicts a configuration in which only the centeraxis l of the inlet 22 is tilted relative to the main body 21. In thisconfiguration, a component that is formed by simple die molding can beused to form the inlet 22 of the main body 21. Accordingly, thisconfiguration is advantageous in that the positional relationshipbetween the center axis l of the inlet 22 and the rotation axis m of theimpeller 3 can be adjusted in a simple and less expensive manner.

FIG. 10 depicts another exemplary configuration in which only therotation axis m of the impeller 3 (the rotation axis of the drive motor4) is tilted relative to the main body 21. This configuration isadvantageous in that the positional relationship between the center axisl of the inlet 22 and the rotation axis m of the impeller 3 can beadjusted in a simple and less expensive manner without changing an outerdimension of the main body 21.

INDUSTRIAL APPLICABILITY

As set forth hereinbefore, a multiblade fan according to the presentinvention is useful in enabling an improvement in noise characteristicsor blowing performance.

EXPLANATIONS OF LETTERS OR NUMERALS

1 multiblade fan, 2 casing, 21 main body, 22 inlet, 23 outlet, 3impeller, 31 blade, 32 main plate, 33 annular member, 4 drive motor

1. A multiblade fan comprising: a scroll type casing that includes a bell-mouthed inlet; and an impeller that includes a plurality of annularly arranged blades and a rotation axis oriented toward the inlet and that is housed in the casing, wherein a center axis of the inlet and the rotation axis of the impeller are arranged to make a tilt angle and in either one of a mutually intersecting positional relationship and a mutually skewed positional relationship, so that a space between the inlet and the impeller is increased from the rotation axis of the impeller toward an outlet of the casing.
 2. The multiblade fan according to claim 1, wherein a positional relationship between the center axis of the inlet and the rotation axis of the impeller is adjusted by arranging the center axis of the inlet to be tilted relative to a main body of the casing.
 3. The multiblade fan according to claim 1, wherein a positional relationship between the center axis of the inlet and the rotation axis of the impeller is adjusted by arranging the rotation axis of the impeller to be tilted relative to a main body of the casing. 